Why does blockchain work only in 1D?

It is pretty interesting to think why current blockchain has to work linearly.

In my viewpoint, I believe this is where blockchain can extend its functionality.

Blockchain gives security and trust, but I think it also takes two things:

1. User data is mixed with others in a single block; ze has to go through the whole chaindata to find UTXOs to get balance
2. Too much memory for Metadatas. They are used too much just for putting all users’ information in a single linked list. For example, bitcoin stores the transaction data with hash in key-value storage and stores those key in the block data. Not only that, the transaction is formed with merkle-tree, because blocks need to be compared without going through each user’s transactions, so extra metadata is added.

These problems happened because all users’ information is mixed in a single blockchain. Why can’t people have their own blockchain so that they can have their own information and get verified on transaction between sender and recipient only? This is rather more decentralized way than current blockchain system.